The ear, being likewise a portal for external impressions, is guarded with equal care. Not a single vibration of air can ever reach the nerve of the ear with the crude intensity (if I may use the expression) with which it is generated. Passing over preliminary apparatus, by which the vibrations of air are first collected, the impressions of sound are first received on the parchment of a little drum, which parchment can be relaxed or tightened with the quickness of thought, so as to modify the force of the impression. This impression is then, by means of a little chain of bones, conveyed across the drum, which is filled with air. It then reaches a portion of the ear in which are found very curious cavities and canals, of various forms, and taking different directions, and which, from the curious and complex arrangement of the whole, is not inappropriately called the labyrinth. This is the mysterious seat of those nerves which convey impressions to the brain. There is, however, here, an arrangement more exquisite than any we have yet mentioned.
In these cavities and canals, which are themselves so small as to be not unfit objects for magnifying glasses, there are corresponding delicate sacs and tubes, and these are filled with a limpid fluid. On this delicate apparatus, so exquisitely calculated to modify any undue force of impression, the sensitive extremities of the auditory nerves are spread out, which convey impressions to the brain. We see, therefore, how carefully these portals of the body are guarded; arrangements equally conservative prevail throughout. We might show a similarly exquisite arrangement in the laws governing the mind; but that is not our present object. We have seen hitherto that, beautiful as the arrangement is for securing us against painful impressions, it has been in a great degree mechanical.
The stomach, however, is the portal to a vast series of important organs, and is protected by a phalanx of sentinels, endowed with powers proportioned to the importance of the organ which they guard. There is little that falls within any idea which we can express by the term mechanical; everything is subjected to an examination essentially sentient; to powers residing in the nerves; the laws and operations of which, we can with proper attention trace out, but which exhibit powers demonstrative of an intensity and refinement of which our limited perceptions scarcely enable us to form a definite idea.
First, there is the olfactory nerve, between which and the stomach there is the most vivid sympathy.
Until our tastes become vitiated, the stomach seldom admits anything of which the nose reports unfavourably. The sense of smell, even in the somewhat measured power possessed by man, is capable of detecting forms of matter so subtle as to be beyond our powers of imagination. Nothing which so plainly deals with "matter" impresses more strongly the immense range which must exist between the chemistry of life and that of the laboratory. We all know the extraordinary powers of musk. I have myself a small mass of odorous matter (a Goa ball) which, from the circumstances under which it came into my possession, must have been emitting the odour for little less than a century. It has been exposed to air, is covered by a film of gold (I believe), is in no respect visibly changed, and for the last thirty years not detectably in weight; yet at this moment it emits as strong an odour of musk as ever. How exquisitely subtle must be the matter thus emitted; or how still more wonderful if it merely so modifies the atoms of air in its neighbourhood as to produce odour. We have no intellectual powers which enable us to realize a conception of such infinite tenuity of matter; yet the sense of smell instantly detects its presence.
Next come the nerves of the tongue; and here again, in natural conditions, there is a constant harmony between them and the stomach—that to which the taste readily gives admission being, in undisturbed conditions of the economy, some guarantee that it is innoxious; but what these functions are to the stomach, the stomach is to the other organs. In the first place, in natural conditions it usually at once rejects any noxious material which, from being disguised, or from any other circumstances, may have eluded the vigilance of the sentinels I have mentioned; but it has a vivid sympathy with every organ in the body. If anything deleterious be once admitted, it has to go through various processes, which may render it a source of indefinite disturbance; therefore, if any organ in the series of the blood-manufacture be materially disturbed—that is, so as to be disabled—the stomach usually refuses food; because there is no other way of stopping the mischief. Illustrations of this occur in many disorders of the kidney, in many affections of the alimentary canal, as also of the liver, and other parts.
No doubt the stomach is therefore a most important organ; but to suppose that it is therefore always the seat of disorder, is not only a most mischievous error, but a complete blind to its most beautiful and instructive relations; and as opposite to Mr. Abernethy's views as the most narrow can be to the most comprehensive. Proceeding with his illustrations, Mr. Abernethy cites a number of most instructive cases, such as palsy and other affections of most serious character, which too often result either from organic disease of some organ, or from mechanical pressure on the brain or spinal marrow, but which in the cases cited depend on disorder of the digestive organs.
It is impossible to exaggerate the interest or importance of these cases; not only from the fact that they almost certainly would have led to organic disease, but also for the value of that practical discrimination which they exemplify. Again, the very treatment which would have been proper, which had sometimes been begun, and which was not inappropriate to cases of organic disease, with which the symptoms were in part identical, would have inevitably, in the cases in question, only served to exasperate the very conditions they were designed to relieve, and to hasten those processes against which they were intended to guard.
No one can understand the force of these cases, without recollecting the intense difficulty of ascertaining that point at which disorder ceases to be merely functional, and at which organic disease begins. This is of all things the most difficult to determine in the whole circle of physiological or pathological inquiry.
The symptoms alone are absolutely useless in any case of real difficulty. Of that Abernethy was well aware, and he did much to guard us against the error into which a reliance on them was calculated to lead. He knew that organs which were diseased would sometimes afford indications not distinguishable from those of health; and that, conversely, organs essentially sound would sometimes only afford those signs which were indicative of disorder. We have, we trust, made some little progress in this very difficult branch of inquiry; and although it is true that organic disease not unfrequently escapes detection during life, yet, so far as we have observed, it is only in those cases in which there is, notwithstanding the daily lessons of experience, an improper reliance on what are called the symptoms. We assert, without the least hesitation, that organic diseases should seldom elude detection where the investigation is sufficiently comprehensive; but it must include all the facts of the case, the early history, and such circumstances which, however remote, have been over and over again proved to be capable of exerting an influence on the body; an investigation which, however vainly pleaded for in medical science, however regarded as too exacting, involves nothing more in principle than is required as a matter of course in all other scientific investigations.